ABSTRACT
Proportional–integral–derivative (PID) control was developed in the early 1940s for controlling processes of the first-order-lag-plus-delay (FOLPD) type. The effect of each term on the closed-loop system is intuitively clear. The proportional term is to affect system error and system stiffness; the integral term is mainly for eliminating the steady-state error; the derivative term is for damping oscillatory response. Two celebrated J. G. Ziegler–N. B. Nichols techniques were developed in the early 1940s for tuning PID control of FOLPD systems. Both techniques have become classics. Details of PID tuning and some further development can be found in Cheng and Hung and Franklin et al. The classical PID techniques have been very useful for process control since many industrial processes can be well approximated by FOLPD models. The classical PID control can make a closed-loop system have a satisfactory damping ratio and zero steady-state error in response to a set-point input.
